1. Field of the Invention
The invention relates to analogue/digital converters, that is to say electronic circuits capable of converting an analogue input signal into an accurate digital value representing the amplitude of the analogue signal. The numerical value is obtained in the form of a word of several bits, coded in pure binary or in some other code.
2. Discussion of the Background
Several conversion processes exist, and the choice of one process rather than another depends on the performance expected of the converter. The most important parameters of this performance are:
resolution, defined by the number of bits of the output word representing with precision the amplitude of the analogue signal; the number of bits can be from 16 to 18, or even 20, for the most accurate converters, and the accuracy is generally plus or minus 1/2 of a lowest-order bit; PA1 speed, that is to say the number of conversion operations which can be performed in one second; PA1 power consumption: a fast and accurate converter consumes much more energy than a slow and inaccurate converter; now, the power consumption causes heating of the integrated circuit chip on which the converter is made. This heating must be compensated for by means of cooling which make the circuit difficult to use when there are bulkiness constraints to be complied with. Moreover, with the proliferation of so-called "portable" equipment (those which operate with the aid of batteries), the "high power consumption" criterion also becomes synonymous with "low lifetime of the equipment"; PA1 and of course the design and fabrication cost of the converter related in particular to the area of the integrated circuit chip used by the converter. PA1 successive-approximation converters, operating relatively slowly; PA1 "flash" converters which use 2.sup.N comparators in parallel, of bulky structure and consuming high power; PA1 interpolation converters, with series structure (several cascaded stages) or parallel structure; PA1 signal-folding converters. PA1 it provides information regarding the position of the voltage Vin with respect to the various reference values; this information serves to establish the high-order bits of the analogue/digital conversion, PA1 and, moreover, at its output it provides folded analogue voltages which can be used by series or parallel interpolation circuits to provide lower-order bits improving the resolution of the analogue/digital conversion. PA1 means for producing n pairs of voltages varying monotonically with Vin, the voltages of a pair of rank k crossing over when Vin has a reference value equal to V.sub.k and varying linearly around their crossover point, the voltages V.sub.k being regularly distributed, PA1 at least two current routing circuits, each of which possesses at least three pairs of inputs and at least two outputs called the direct output and the inverse output,
The qualities of an analogue/digital converter result from a compromise between the above parameters and an objective of the present invention is to improve this compromise.
Among the known structures of analogue/digital converters may be cited: